An insulated gate bipolar transistor (IGBT) has been known as an example of a power semiconductor device. For example, the IGBT includes a p-type collector region, an n base region, and a p base region which are provided on a collector electrode. In addition, a trench gate electrode is provided in a trench that passes through the p base region and reaches the n base region, with a trench gate insulating film interposed therebetween. Furthermore, an emitter region connected to an emitter electrode is provided in a region that is adjacent to the trench in the surface of the p base region.
In the IGBT, a positive voltage is applied to a gate electrode to form a channel in the p base region. Then, holes are injected from the collector region to the n base region at the same time as electrons are injected from the emitter region to the n base region. Then, a current flows between the collector electrode and the emitter electrode.
A method for preventing holes from being emitted from the n base region has been known in order to reduce on-resistance between the collector electrode and the emitter electrode of the IGBT. In this method, the emission of holes from the n base region to the emitter electrode is prevented to increase the relative number of electrons injected and to reduce the on-resistance of the IGBT.
For example, in order to achieve the method, a thinning out-type IGBT has been proposed in which a dummy trench gate electrode that does not contribute to the formation of a channel is provided between trench gate electrodes. It is preferable to achieve a thinning out-type IGBT with improved characteristics such as a high switching speed and low on-resistance.